Compared with other types of valves, wafer gate valves have advantages due to their very small overall length and their reliability in use with various flow media, especially thick substances, which ensure that they are used in certain applications, particularly in industrial processing. The seal between the valve casing and the valve disc is made by means of a soft packing gasket. In the known constructional valve forms, this packing gasket is placed between the two halves of a split valve casing. However, it is then necessary to also seal the joint between both casing halves which, due to the large sealing surface, limits the use of such valves to small pressures. In addition, long machining times are required. These disadvantages are not present for a valve with a one-part valve casing. However, for such valves the soft packing gasket must be arranged in the valve casing in such a way that on the one hand it is reliably secured therein, so that it is not torn out by the flow forces occurring in the valve channel, particularly on partially opening the valve, and on the other it also provides a completely satisfactory seal with the valve casing.
In a known gate valve (French Pat. No. 1,467,759), a slot provided with an O-ring seal is located in a one-part valve casing. However, the O-ring is not secured in a reliable manner, so that it can be torn out under certain valve operating conditions.
In order to obviate this disadvantage, it is known (German Pat. No. 1,750,594), while utilizing the advantage of a one-part valve casing with an unmachined slot for receiving the soft packing, to use additional retaining means in order to hold the packing in form-locked manner in the slot. For this purpose the soft packing on one side of the relatively large slot is engaged on a contact surface arranged at right angles and somewhat inclined relative to the flow channel axis. On the opposite side of the soft packing there is provided a U-shaped fillet and the packing is pressed onto the contact surface by screws. To ensure that the soft packing cannot be displaced outwards, it is also at least partly secured by a web on its outer periphery, whereby the flange is pressed by screws against the packing. This admittedly provides a reliable soft packing, but such a structure is relatively expensive.
It would be desirable to improve a gate valve of the type described above, so that the soft packing is held in a simple, reliable and form-locked manner and preferably in an unmachined slot and for a casing of either one or two parts.